A multi-channel switching device usually includes one power semiconductor switch (usually a MOSFET) per output channel wherein an electric load is connected to each output channel. Thus, each electric load may be switched on and off using the respective semiconductor switch. For example, an on-resistance of 100 mΩ and a nominal load current of 1 A can result in a power loss of 100 mW for each active output channel of the power semiconductor switch. Each power semiconductor switch has usually a reverse diode coupled in parallel to the load current path of the semiconductor switch (e.g., the drain-source path in case of a MOSFET). During normal operation, which entails positive supply voltages up to 60 V, this reverse diode is reverse biased and in a blocking state. However, when a negative supply voltage is applied, the reverse diode becomes forward biased and load current may be directed form ground through the load and the reverse diode to the negative supply potential. Assuming a diode forward voltage of at least 0.7 V the resulting power loss in the reverse diode (and thus in the switching device) is 700 mW per output channel, at least seven times more as during normal operation. Such a situation may be hazardous for the switching device and appropriate reverse polarity protection circuitry is required. Generally, the current between the supply terminal and the ground terminal of the semiconductor device should be limited to a few milliamperes in the case of reverse polarity (e.g., negative supply voltages of −16 V or more). However, an overvoltage (e.g., positive supply voltages of more than 60 V or negative supply voltages of less than −16 V) may occur at the supply terminals of a switching device due to electrostatic discharge (ESD) or the like. In such events, a low resistive current path should be provided to dissipate the energy and clamp the voltages to defined limits.
Known circuitry providing reverse polarity protection and ESD protection to smart semiconductor switches is comparably complex and requires significant chip space. Thus, there is a need for a smart semiconductor switch including an efficient reverse polarity protection (as far as circuit complexity and chip space requirement are concerned).